The Rain Song is classic Led Zeppelin: big guitars, lush chords, and orchestration for days. Jimmy Page uses his full bag of tricks on this song, including one of his favorite tricks of all time: using alternate guitar tunings. If you want to get that lush guitar sound then you need to learn how to tune your guitar for The Rain Song. So strap on and plug in.
Double check the tuning of the D, A and E strings (the fourth, fifth and sixth strings). You won't have to alter the sounding pitch of these three strings, but its a good idea to check before you begin re-tuning.
Raise the pitch of the G string
Drop the pitch on the B string